1. Field of the Invention
The present invention relates to the acquisition of information stored on a medium requiring physical movement to retrieve. More specifically, the present invention relates to the control of driving mechanisms to synchronize the acquisition of data on different media.
2. Description of the Prior Art
In the field of audio post-production for video, as well as music recording for records and film, it is often necessary to create and maintain a very precise positional and speed lock between two or more tape recorders that contain various audio and video information. Often, it is desirable for this information to be recorded and produced in synchronization in a fashion that is more or less automatic with respect to the equipment operator. That is, the operator desires to have a simultaneous presentation of the material recorded on several machines, yet wishes to operate the transport controls of only one.
This kind of operation has traditionally been accomplished via a piece of equipment known as an edit-code chase synchronizer. This device, in its simplest implementation, reads the special address code known as SMPTE time-code, that has been previously recorded on the address tracks of the master and slave tape recorders. The synchronizer then generates for the slave transport rewind, fast-forward, stop, play and capstan speed command signals in such a fashion as to make the slave tape recorder follow the master recorder as closely as possible.
Many difficulties exist in creating a synchronizer which operates optimally. For example, a master tape transport is often capable of being moved to a new location much faster than the slave can catch up due to tape reel inertia in the slave. This is particularly the case when the master must be moved some substantial distance from its previous location, for example, from the end to the beginning of a piece of music or dialogue. When the master is moved to some position that is several minutes away from the position of the slave, prior art chase synchronizers often cannot relocate the slave to the master's new position except by overshooting its destination several times, and even then can locate only to within about several frames of time-code, or about five inches of tape.
In addition, except when the master was in its play mode, prior equipment had limitations with respect to how close the slave could follow the master, particularly when the reels of the master were being slowly rotated by hand after the slave had parked at the master's position. Typically, there existed a positional slave error of at least several seconds of tape, with the slave speed varying erratically above and below the master speed by as much as 200%. Close lock (50 microsecond) was possible only in the forward direction at or near play speed.
These limitations are significant in at least two instances. Many times, an operator turns a video recorder by hand and desires an audio recorder to be aligned. In such a situation, the amount of relative positional error induced by prior art synchronizers makes editing judgments inaccurate. At other times, particularly after fast winding operations, an operator was forced to wait for the slave transport to "settle down" or end its hunting before being able to continue with the editing process.